The present invention relates to a non-contact power transmission apparatus, and more particularly to a resonance type non-contact power transmission apparatus.
FIG. 9 schematically shows a resonance type non-contact power transmission apparatus that transmits power from a first copper wire coil 51 to a second copper wire coil 52 placed at a distance from the first copper wire coil 51 by means of resonance of electromagnetic fields. Such an apparatus is disclosed, for example, in NIKKEI ELECTRONICS published on Dec. 3, 2007, pages 117 to 128 and International Patent Publication No. WO/2007/008646. In FIG. 9, a magnetic field generated at a primary coil 54 connected to an AC power source 53 is enhanced by magnetic field resonance by the first and second copper wire coils 51, 52, so that electrical power is generated at a secondary coil 55 through electromagnetic induction of the enhanced magnetic field of the second copper wire coil 52. The generated power is then supplied to a load 56. It has been observed that a 60-watt electric lamp, as the load 56, can be lit when first and second copper wire coils 51, 52 having a diameter of 30 cm are separated by 2 m.
To efficiently supply output power of the AC power source 53 to the load 56 in this resonance type non-contact power transmission apparatus, it is necessary to supply power from the primary coil 54 to the first copper wire coil 51 on the transmission side at a resonance frequency of the first copper wire coil 51 on the transmission side and the second copper wire coil 52 on the reception side. However, the above cited documents only disclose summaries of non-contact power transmission apparatuses, but do not specifically show what should be done to obtain a non-contact power transmission apparatus that satisfies the requirements.
Also, to efficiently supply the output power of the AC power source 53 to the load 56 using the resonance type non-contact power transmission apparatus, it is necessary to supply the output power of the AC power source 53 to the resonance system (the first and second copper wire coils 51, 52 and the primary and secondary coils 54, 55). In a case where an AC voltage having a certain frequency is output from the AC power source 53 to transmit power to the load 56, the power transmission efficiency changes if the distance between the resonance coils, that is distance between the first and second copper wire coils 51, 52, is changed. Therefore, in a case of a non-contact power transmission apparatus used in a condition where the distance between the first copper wire coil 51 on the transmission side and the second copper wire coil 52 on the reception side can vary, for example, in a case where the second copper wire coil 52 on the reception side is mounted on a movable body such as a vehicle or a robot, power transmission needs to be carried out in a state where the movable body is stopped at a position where the distance between the resonance coils allows power transmission to be efficiently carried out. However, if a dedicated sensor is provided for measuring the distance between the resonance coils, the manufacture becomes troublesome and the size of the apparatus is increased, accordingly.